PLoS One. 2015 Mar 25;10(3):e0121643.

The effect of daily Co-trimoxazole prophylaxis on natural development of antibody-mediated immunity against P. falciparum malaria infection in HIV-exposed uninfected Malawian Children.

Herbert Longwe1, Kondwani C. Jambo2, Kamija S. Phiri3, Nyanyiwe Mbeye4, Thandile Gondwe4, Tom Hall5, Kevin K. A. Tetteh5, Chris Drakeley5, Wilson L. Mandala1,2

1Department of Basic Medical Sciences, College of Medicine, University of Malawi, Blantyre, Malawi

2 Malawi-Liverpool-Wellcome Trust Clinical Research Programme, Blantyre, Malawi

3Tropical Haematology Research Unit, College of Medicine, University of Malawi, Blantyre, Malawi

4Department of Public Health, College of Medicine, University of Malawi, Blantyre, Malawi

5London School of Hygiene and Tropical Medicine, London, United Kingdom

 

Abstract

Objectives: Co-trimoxazole prophylaxis, currently recommended in HIV-exposed, uninfected (HEU) children as protection against opportunistic infections, also has some anti-malarial efficacy. We determined whether daily co-trimoxazole prophylaxis affects the natural development of antibody-mediated immunity to blood-stage Plasmodium falciparum malaria infection.

Methods: Using an enzyme-linked immunosorbent assay, we measured antibodies to 8Plasmodium falciparum antigens (AMA-1, MSP-119, MSP-3, PfSE, EBA-175RII, GLURP R0, GLURP R2 and CSP) in serum samples from 33 HEU children and 31 HIV-unexposed, uninfected (HUU) children, collected at 6, 12 and 18 months of age.

Results: Compared to HIV-uninfected children, HEU children had significantly lower levels of specific IgG against AMA-1 at 6 months (p = 0.001), MSP-119 at 12 months (p = 0.041) and PfSE at 6 months (p = 0.038), 12 months (p = 0.0012) and 18 months (p = 0.0097). No differences in the IgG antibody responses against the rest of the antigens were observed between the two groups at all time points. The breadth of specificity of IgG response was reduced in HEU children compared to HUU children during the follow up period.

Conclusions: Co-trimoxazole prophylaxis seems to reduce IgG antibody responses to P. falciparum blood stage antigens, which could be as a result of a reduction in exposure of those children under this regime. Although antibody responses were regarded as markers of exposure in this study, further studies are required to establish whether these responses are correlated in any way to clinical immunity to malaria.

 

Supplementary

Plasmodium falciparum malaria infection is still one of the main causes of under-five child morbidity and mortality in Sub-Saharan Africa [1] with an annual estimate of 216 million episodes of malaria worldwide, 174 million cases occurring in sub Saharan Africa, resulting in about 660,000 deaths mainly in children under-five [2]. Several factors are thought to be responsible for this high mortality rate [3], with the host immune response to the infection playing a crucial role [4]. Naturally acquired antibodies to P. falciparum are protective against malaria infection [5,6]. In children, malaria-specific immunity develops slowly and is dependent on repeated exposure [7] with naturally acquired IgG responses to some P. falciparum associated with reduced incidence of malaria [8].

Co-trimoxazole (CTX), due to its antibiotic efficacy, is recommended for prophylactic treatment in HIV-infected children [9] and in HIV-uninfected but exposed (HEU) children (born to mothers living with HIV) [10]. CTX is also known to be an effective anti-malarial drug [11]. Malaria chemoprophylaxis that involves the use of malaria-specific drugs in young children has been found to impair the development of the host’s natural immunity against malaria thereby increasing the child’s susceptibility to malaria when the intervention is stopped [12]. Although CTX is not prescribed as a malaria chemoprophylaxis in HEU children, we wanted to find out if its anti-malarial effects could have a similar effect on the development of natural immunity. We therefore conducted this study to investigate the effects of daily CTX prophylaxis on the magnitude and breadth of IgG antibody responses against P. falciparum blood stage antigens in HEU children (n = 33) in Zomba, Malawi. With the assumption that P. falciparum transmission is heterogeneous even within small geographical areas [13], HIV-unexposed uninfected (HUU) children (n = 31) from the same communities of HEU children were recruited as controls.

We recruited HEU children, who received daily CTX prophylaxis from 6 weeks to 12 months, and HUU children from 6 months of age and followed them up until they were 18 months old. Children were seen every six months and at each visit and their blood analysed for parasitaemia and antibody levels against P. falciparum antigens. The study was reviewed and approved by the College of Medicine Research Ethics Committee (COMREC) (P.05/10/954). Individual written informed consent was obtained from the parents or guardians of the children who participated in the study.

 

WM FIG1

Figure 1: Specific IgG responses to P. falciparum antigen in HEU and HUU children at different ages: Levels of specific IgG titres (geometric means and 95% confidence interval) were measured against PfSE in HEU and HUU at three time points, 6 months (during CTX prophylaxis), 12 months (At stopping CTX prophylaxis) and 18 months (6 months after CTX prophylaxis).

 

Although similar number of children in ach group (n = 2) presented with uncomplicated malaria during study, significant variations of antibody concentrations over time were determined in both study groups. IgG antibody responses against CSP in HE, but not HUU, children showed a steady increase from 6 to 12 months and 6 to 18 months. Among HEU children, there was an increase in the IgG antibody titres from baseline against MSP-3 from 6 to 12 months.

HEU children had significantly low levels of IgG antibody titres to PfSE compared to HUU children at 6 months, at 12 months and at 18 months (Fig. 1).

At six months of age, HEU children had significantly lower levels of IgG antibody titers to AMA-1 compared to HUU children (Fig. 2) and to MSP-119 at 12 months of age compared to HUU children (Fig. 3). These results suggest that the magnitude of malaria antibody titers is lower in HEU infants possibly due to lower exposure to malaria due to the effect of CTX prophylaxis or due to HIV induced impairment of antibody immunity.

 

WM FIG2

Figure 2: Specific IgG responses to AMA-1 antigen in HEU and HUU children at different ages: Levels of specific IgG titres were measured against AMA-1 in HEU and HUU at 6 months (during CTX prophylaxis), 12 months (At stopping CTX prophylaxis) and 18 months (6 months after CTX prophylaxis).

 

In order to measure the potential confounding effect of in-utero exposure to HIV, we measured IgG responses to Bordetella pertussis toxin (PT) in HEU children and compared with IgG responses from HUU children. HEU children had significantly higher levels IgG antibody titers against PT compared to HUU children at all three age stages.

These results suggest that the difference seen between malaria antibody responses over time between HEU and HUU are not HIV-mediated but rather reduction in malaria exposure in the HEU infants due to CTX prophylaxis.

 

WM FIG3

Figure 3: Specific IgG responses to MSP-1 antigen in HEU and HUU children at different ages: Levels of specific IgG titres were measured against MSP-1 in HEU and HUU at 6 months (during CTX prophylaxis), 12 months (At stopping CTX prophylaxis) and 18 months (6 months after CTX prophylaxis).

 

In summary, we investigated the effect of daily CTX prophylaxis on the acquisition of malaria specific IgG antibodies during the first year of life in a cohort of HEU Malawian children and found that HEU children on CTX prophylaxis had reduced specific IgG antibody responses to the following malaria blood stage antigens; AMA-1, MSP-119 and whole parasite extract PfSE when compared to HUU children not receiving prophylaxis. IgG antibody responses to the other recombinant blood stage antigens were not significantly different between HEU and HUU children during the entire follow up period. These results are consistent with findings of previous studies [14].

 

WM FIG4

Figure 4: Specific IgG responses to Bordetella pertussis toxin (PT) antigen in HEU and HUU children at different ages. Levels of specific IgG titres were measured against P in HEU and HUU at 6 months (during CTX prophylaxis), 12 months (At stopping CTX prophylaxis) and 18 months (6 months after CTX prophylaxis).

 

Importance of the study

The findings of this study provide additional evidence that the use of CTX prophylaxis in the first year of life interferes with acquisition of natural antibody responses to blood stage malaria antigens. Given that the antibody responses observed in this study were markers of exposure, it remains to be established whether the delay in acquisition of these specific antibody responses translates into increased risk of malaria infection in HEU exposed to CTX prophylaxis.

 

Acknowledgements

The study was funded by HRCSI, a DFID and Wellcome Trust funded programme and the HIV Research Trust UK, CARTA, and SACORE both of which were Wellcome Trust funded African Institutions Initiatives.

 

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WM AUTHORCorresponding author

Wilson Mandala PhD,

College of Medicine, University of Malawi,

P/Bag 360, Blantyre, Malawi

Email: wmandala2002@gmail.com

Tel: +265 995 450 785, Fax: +265 1 874 700

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